Zirconia base ceramics

Abstract

The invention consists of zirconia base with high hydrothermal stability which: (a) consists essentially of at least 40 weight % of partially stabilized zirconia of the ZrO 2 -Y 2 O 3 -CeO 2 system wherein the proportion of ZrO 2 , Y 2 O 3 , and CeO 2 is within the range defined by the line connecting points F, G, L, M, N and K in a ternary diagram (ZrO 2 , YO 1 .5, CeO 2 ), the vertices of said points being given by the following molar % of ZrO 2 , YO 1 .5, and CeO 2 , respectively: F (88, 10, 2), G (89, 10, 1), L (93.5, 4, 2.5), M (93, 2, 5), N (88, 1, 11), and K (86, 1,13), and 3 to 60 weight % of at least one of Al 2 O 3 , MgO.Al 2 O 3 , spinel and mullite, and (b) has a mean crystal grain size not exceeding 2 micrometers and a bending strength of at least 100 kgf/mm 2 , said ZrO 2 containing a minimum of 50 volume % tetragonal crystal structure and a maximum of 5 volume % monoclinic crystal structure when tested in steam of 180° C. and 10 atm for 10 hours. The monoclinic crystal structure does not exceed 5 volume % when tested in an atmosphere of 300° C. for 3000 hours. These zirconia base ceramics are stable in the presence of moisture under low temperatures of approximately 200°-400° C.

What is claimed is: 
     
       1. Zirconia base ceramics which: (a) consist essentially of at least 40 weight % of paritally stabilized zirconia of the ZrO 2  -Y 2  O 3  -CeO 2  system wherein the proportion of ZrO 2 , Y 2  O 3  and CeO 2  is within the range defined by the line connecting points F, G, L, M, N, and K in a ternary diagram (ZrO 2 , YO 1 .5, CeO 2 ), the vertices of said points being given by the following molar % of ZrO 2 , YO 1 .5 and CeO 2 , respectively:   F (88, 10, 2),   G (89, 10, 1),   L (93.5, 4, 2.5),   M (93, 2, 5),   N (88, 1, 11), and   K (86, 1, 13), and 3 to 60 weight % of Al 2  O 3 , and     (b) has a mean crystal grain size not exceeding 2 micrometers and a bending strength of at least 100 kgf/mm 2 , said ZrO 2  containing a minimum of 50 vol % tetragonal crystal structure and a maximum of 5 vol % monoclinic crystal structure when tested in steam of 180° C. and 10 atm for 10 hours.   
     
     
       2. Zirconia base ceramics as defined in claim 1, which has quantity of said monoclinic crystal structure not exceeding 5 vol % when tested in an atmosphere of 300° C. for 3000 hours. 
     
     
       3. Zirconia base ceramics as defined in claim 1, wherein the amount of Al 2  O 3  is 5 to 50 weight %. 
     
     
       4. Zirconia base ceramics as defined in claim 3, wherein the amount of Al 2  O 3  is 15 to 35 weight %. 
     
     
       5. Zirconia base ceramics which: (a) consists essentially of at least 40 weight % of partially stabilized zirconia of the ZrO 2  -Y 2  O 3  -CeO 2  system wherein the proportion of ZrO 2 , Y 2  O 3  and CeO 2  is within the range defined by the line connecting points F, G, L, M, N and K in a ternary diagram (ZrO 2 , YO 1 .5, CeO 2 ), the vertices of said points being given by the following molar % of ZrO 2 , YO 1 .5 and CeO 2 , respectively:   F (88, 10, 2),   G (89, 10, 1),   L (93.5, 4, 2.5),   M (93, 2, 5),   N (88, 1, 11), and   K (86, 1, 13), and 3 to 60 weight % of MgO.Al 2  O 3  spinel, and     (b) has a means crystal grain size not exceeding 2 micromenters and a bending strength of a least 100 kgf/mm 2 , said ZrO 2  containing a minimum of 50 vol % tetragonal crystal structure and a maximum of 5 vol % monoclinic crystal structure when tested in steam of 180° C. and 10 atm for 10 hours.   
     
     
       6. Zirconia base ceramics as defined in claim 5, which have a quantity of said monoclinic crystal structure not exceeding 5 vol % when tested in an atmosphere of 300° C. for 3000 hours. 
     
     
       7. Zirconia base ceramics as defined in claim 10, which have a quantity of said monoclinic crystal structure not exceeding 30 vol % when tested in a sulfuric solution for 100 hours. 
     
     
       8. Zirconia base ceramics as defined in claim 5, wherein the amount of MgO.Al 2  O 3  spinel is 5 to 50 weight %. 
     
     
       9. Zirconia base ceramics as defined in claim 8, wherein the amount of MgO.Al 2  O 3  spinel is 15 to 35 weight %. 
     
     
       10. Zirconia base ceramics as defined in claim 5, wherein a part of the MgO.Al 2  O 3  spinel is replaced by Al 2  O 3 . 
     
     
       11. Zirconia base ceramics which: (a) consists essentially of at least 40 weight % of patially stabilized zirconia of the ZrO 2  -Y 2  O 3  -CeO 2  system wherein the proportion of ZrO 2 , Y 2  O 3  and CeO 2  is within the range defined by the line connecting points F, G, L, M, N and K in a ternary diagram (ZrO 2 , YO 1 .5, CeO 2 ), the vertices of said points being given by the following molar % of ZrO 2 , YO 1 .5 and CeO 2 , respectively:   F (88, 10, 2),   G (89, 10, 1),   L (93.5, 4, 2.5),   M (93, 2, 5),   N (88, 1, 11), and   K (86, 1, 13), and 3 to 60 weight % of mullite, and     (b) has a mean crystal grain size not exceeding 2 micrometers and a bending strength of at least 100 kgf/mm 2 , said ZrO 2  containing a minimum of 50 vol % tetragonal crystal structure and a maximum of 5 vol % monoclinic crystal structure when tested in steam of 180° C. and 10 atm for 10 hours.   
     
     
       12. Zirconia base ceramics as defined in claim 11, which have a quantity of said monoclinic crystal structure not exceeding 5 vol % when tested in an atmosphere of 300° C. for 3000 hours. 
     
     
       13. Zirconia base ceramics as defined in claim 11, wherein the amount of mullite is 5 to 50 weight %. 
     
     
       14. Zirconia base ceramics as defined in claim 13, wherein the amount of mullite is 15 to 35 weight %. 
     
     
       15. Zirconia base ceramics as defined in claim 11, wherein the bending strength at 500° C. is at least 50 kgf/mm 2 . 
     
     
       16. Zirconia base ceramics as defined in claim 11, wherein the mullite amount is at least 10 weight % and the coefficient of the linear thermal expansion is 1×10 -5  ° C. -1  or less. 
     
     
       17. Zirconia base ceramics as defined in claim 11, wherein a part of the mullite is replaced by Al 2  O 3 . 
     
     
       18. Zirconia base ceramics which: (a) consists essentially of at least 40 weight % of partially stabilized zirconia of the ZrO 2  -Y 2  O 3  -CeO 2  system wherein the proportion of ZrO 2 , Y 2  O 3  and CeO 2  is within the range defined by the line connecting points F, G, L, M, N and K in a ternary diagram (ZrO 2 , YO 1 .5, CeO 2 ), the vertices of said points being given by the following molar % of ZrO 2 , YO 1 .5, and CeO 2 , respectively:   F (88, 10, 2),   G (89, 10, 1),   L (93.5, 4, 2.5),   M (93, 2, 5),   N (88, 1, 11), and   K (86, 1, 13), and 5 to 60 weight % of the sum of MgO.Al 2  O 3  spinel and mullite, provided that any one of the spinel and mullite is 3 weight % or more, and     (b) has a mean crystal grain size not exceeding 2 micrometers and a bending strength of at least 100 kgf/mm 2 , said ZrO 2  containing a minimum of 50 vol % tetragnal crystal structure and a maximum of 5 vol % monoclinic crystal structure when tested in steam of 180° C. and 10 atm for 10 hours.   
     
     
       19. Zirconia base ceramics as defined in claim 18, which have a quantity of said monoclinic crystal structure not exceeding 5 vol % when tested in an atmosphere of 300° C. for 3000 hours. 
     
     
       20. Zirconia base ceramics as defined in claim 18, wherein the sum of the MgO.Al 2  O 3  spinel and mullite is 50 weight % or less. 
     
     
       21. Zirconia base ceramics as defined in claim 20, wherein the sum of the MgO.Al 2  O 3  spinel and mullite is 15 to 35 weight % 
     
     
       22. Zirconia base ceramics as defined in claim 16, wherein the amount of mullite is at least 10 weight %. 
     
     
       23. Zironia base ceramics as defined in claim 20, wherein the bending strength at 500° C. is at least 60 kgf/mm 2 . 
     
     
       24. Zirconia base ceramics as defined in claim 20, wherein the coefficient of linear thermal expansion between 25° and 1000° C. is 1×10 -5  ° C. -1  or less. 
     
     
       25. Zirconia base ceramics as defined in claim 18, wherein the amount of the MgO.Al 2  O 3  spinel is at least 10 weight %. 
     
     
       26. Zirconia base ceramics according to claims 1, 5, or 18, wherein ZrO 2  does not exceed 92% in the ternary diagram of FIG. 1.